<script>
    //回调地狱 (生成器，promise)
    //1秒aaa,aaa后2秒bbb,bbb后3秒ccc
    setTimeout(() => {
        console.log("aaa");
        setTimeout(() => {
            console.log("bbb");
            setTimeout(() => {
                console.log("ccc");
            }, 3000);
        }, 2000);
    }, 1000);
</script>